Advanced Materials Research Vols. 243-249

Abstract: Based on beam specimens of 100mm×100mm×400mm, the effect of electrochemical chloride extraction (ECE) on bond performance between steel bar and concrete contaminated by chloride was studied by determining the bond strength of them. During the test, 1%, 2% and 3% NaCl by weight of cement were mixed into concrete to simulate chloride contamination. In the process of ECE, four kinds of current density (1, 2, 3, 5 A/m² of steel bar area) and electric quantity (500, 1000, 1500 and 3000 A.h/m² of steel bar area) were taken into account, respectively. It is indicated that the bond strength between steel bar and concrete was degraded after ECE treatment, the more the current and the electric quantity of ECE are, the more the loss of bond strength is, and the initial content of chloride in concrete has a little influence on the bond strength.

Abstract: Fiber reinforced plastics (FRP) has been widely used in structure reinforcement processing. It is a comparatively mature field in computational models of cylindrical axial compressive strength on FRP confined concrete. In this paper, we conduct a possessive analysis on the axial compressive property that is based on the cylindrical stress model of FRP confined concrete, considering the difference among square column section, rectangular column and cylindrical column. Meanwhile, based on cross-sectional area and moment of inertia equivalent principles, we propose an equivalent diameter formula for converting rectangular column section into cylindrical column section. We also introduce sectional influence coefficients to modify ultimate strength and establish a model of ultimate strength for FRP confined concrete. Furthermore, we use the existing experimental data to test the validity and feasibility of the model. Experimental Results of the computational model are quite coincident and consistent with the tests. Computational model can reflect the true characteristics of FRP confined concrete. Therefore, the models proposed in this paper are significant in the practice of construction project.

Abstract: The method of seismic strengthening the RC frame T-shaped joints with FRP was designed. Its significant effect of seismic reinforcement was verified through cyclic loading tests. The joints models were established using finite element analysis software ANSYS. The whole process of monotonic loading at the beam end were simulated numerically in order to study in depth of the mechanism of FRP reinforcement. Experimental results and numerical simulation analysis showed that: fibers wrapped in the core area of the joints could improve the strength of concrete, and bear part shear of the joints; bending fibers at the beam-column end played to take parts of the moment and reduce the stress of longitudinal bars in the corresponding parts, thus improving indirectly the bearing capacity and ductility of the members strengthened using FRP increased; the stiffness of the joints strengthened with FRP increased when identical loading.

Abstract: Because of the change of using function of one masonry structure, its longitudinal walls need to be underpinned. The related members also need to be reinforced. This paper has a discussion on the thought of underpinning part, strengthening method and key construction process. They main involve the reinforcement of foundation, the transformation from non-bearing members to bearing members of ring beams and constructional columns. It also involves the construction points for attention during underpinning process. At last, the main points that shuold be paid attention to in strengthening deign and underpinning construction are concluded.

Abstract: After a long period time of working, an auxiliary shaft RC headframe in a colliery got series quality problems, such as the concrete carbonation of the RC members, the concrete loosen and spalling, the exposed steel bar, steel corrosion and the degradation of the bond quality. After making a detailed operating environment and safety detection and evaluation, we studied the deterioration mechanism and the rehabilitation and strengthening technology. Considering that the headframe belongs to the special structures of colliery, we emphatically introduced the strengthening design method and process in order to provide the similar reinforcement project with a reference.

Abstract: In this paper, the feasibility of inhibitor auxiliary re-alkalization was investigated. The effect of realkalization auxiliary inhibitor repair technique was studied by simulative experiment. It studied the changes of electrochemical parameters of the natural carbonated reinforced concrete during the electrochemical realkalization in 1mol/L Na₂CO₃ solution and the mixed solution of 1mol/L Na₂CO₃ and 1 mol/L DMEA , as well as the impedance spectroscopy and polarization curves in the process of relaxation. The results showed that: there appears to be no effect of DMEA on the corrosion potential and the impedance of the steel in the process of realkalization. That was, the performance was the same as that in the sodium carbonate solution except corrosion current of rebar with DMEA which showed much lower. But of the samples which the DMEA existed in the electrolyte was significantly shorter at the same relaxation time after realkalization. At the same relaxation time the corrosion potential was more positive and the corrosion current density was smaller. It improved significantly the effect of realkalization.

Abstract: The use of fiber reinforced polymers (FRP) to reinforce reinforced concrete(RC) structure has become one of the main applications of composites in civil engineering. FRP composite is analyzed using the serial/parallel mixing theory, which deduces the composite behavior from the constitutive equations of its components. Numerical procedure of RC beam reinforceed with FRP is studied based on the finite element method. The numerical results accord with the test results. The validity of the proposed procedure is proved comparing numerical and experimental results.

Abstract: The resisting shear strengthening technology of existing reinforced concrete bridges as an important research topic in the field of old bridges, play an important significance to improve the mechanical properties of old bridges and reduce security incidents. Based on comparative test analysis on two basic beams and twelve reinforced concrete beams strengthened with external pre-stressed wire rope, the influence of the shear strengthening effect was studied systematically caused by the original beam design parameters and the spacing of wire rope, in the meantime the strengthening mechanism was analyzed. Research results showed that the shear capacity of the strengthened beams was improved, because the development of cracks was not only effectively limited, but also stirrup strain was reduced, and yield load was put off. Along with the increasing of the ratio of original beams longitudinal reinforcement and the ratio of stirrup ,and the concrete grade, as well as the decreasing of spacing of external wire rope, the stirrups strain were decreasing and the shear capacity of strengthened beams increased. With the spacing of external wire rope decreasing, the diagonal crack resistance of the strengthened beams increased. The research results can provide reference for the design and research on shear strengthening of bridges.

Abstract: Ability insufficiently in shear is one of common trouble of old RC (reinforced concrete) beams, so scientific and reasonable shear resistant reinforcement method is one of the important research topics in the old bridge reinforcement and rehabilitation fields, and is of great significance in improving old bridge’s mechanical properties and reducing safe accidents. The shear resistant strengthening effect of strengthened beams with SWR (steel wire rope) external prestressing is studied under different dead load level and damage degree when strengthening, through the indoor experiment in shear. The results of the experiment shows: the width of diagonal cracks of the beams strengthened with SWR external prestressing become smaller and the yield load of stirrups is delayed, and the shear capacity is improved compared with basic beam. Both dead load level when strengthening and damage degree of original beams are the important factors influencing the shear resistant reinforcement effect , and with increasing of the dead load level and damage degree when strengthening, the improved amplitude of the yield load of stirrups and the shear bearing capacity are getting decreasing. The dead load level and damage degree when strengthening should be taken into account.

Abstract: Rehabilitation of RC members with stainless steel wire mesh and permeability polymer mortar is a new method of structural strengthening with the advantages of resistance to fire, corrosion and ageing. Experiments were conducted to investigate the shear behavior of eight strengthened RC rectangular beams and one comparative RC beam. The shear mechanism of strengthened beams was analyzed, and the influences of the strengthening manners, bolts’ amount, bolts’ distance on the shear behavior of strengthened beams were discussed. The test results show that the rehabilitation greatly increase the beam’s shear load-carrying capacity, shear stiffness, and its ductility. But the range of load capacity improvement is greatly influenced by the bolts’ amount and distance, too much and dense bolts badly weaken the shear behavior of beam itself. The influences of the strengthening manners on the load capacity are puny, but the beams’ failure modes are different.